Hydraulic aggregates for the powering of heavy machinery have a prime mover, such as an internal combustion engine, whose output shaft drives a plurality of pumps, including at least one variable-displacement pump and at least one constant-displacement pump, have been provided heretofore as described, for example, in HIGHPRESSURE HYDRAULICS ON EUROPEAN EXCAVATORS, by Hans-Dieter KNOLKER, published by Linde AG, Werksgruppe Guldner Aschaffenburg, Germany, (FIG. 13 and page 6).
Such systems do not respond adequately to the control arrangements which have hitherto been provided and, more particularly, do not respond effectively to drops in the output speed of the prime mover or energy source.